Probing the mechanism of the carcinogenic activation of N-nitrosodiethanolamine with deuterium isotope effects: in vivo induction of DNA single-strand breaks and related in vitro assays.

A series of bioassays, including in vivo induction of DNA single-strand breaks (SSB) and cytotoxicity in cytochrome P450 2E1-transfected cells, were utilized with N-nitrosodiethanolamine (NDELA), its deuterated isotopomers (α-D4NDELA and β-D4NDELA), N-nitroso-2-hydroxymorpholine (NHMOR), and two of its deuterated isotopomers (2-D-NHMOR and 5,5-D2-NHMOR) to probe the mechanism of carcinogenic activation of NDELA and the role of its metabolite NHMOR. DNA samples, taken from the livers of male Wistar rats 4 h after the administration of NDELA, exhibited dose-dependent DNA SSB levels over the range of 0.08−0.75 mmol/kg (body weight), with the greatest SSB level at the highest dose. Deuterium isotope effects on DNA SSB levels were inversely dependent on dose:  α-D4NDELA, 3.22−1.37; and β-D4NDELA, 1.38−0.79. At the lowest dose of 0.15 mmol/kg (body weight), 5,5-D2-NHMOR gave an isotope effect for DNA SSB of 2.8 while that for 2-D-NHMOR was 0.7. NDELA and β-D4NDELA were equally cytotoxic to human P450 2E1-transf...